BARCELONA — Spanish Prime Minister Mariano Rajoy on Wednesday took the first step towards activating a so-called nuclear option in the country's constitution that would allow him to suspend Catalonia's political autonomy and take over the region.Rajoy held an emergency cabinet meeting the morning after the leader of the autonomous region, Carles Puigdemont, balked at making a formal declaration of independence from Spain in a much-anticipated speech to the Catalan parliament on Tuesday.